Dual clutch manual transmissions, as they are often called, have two selectively engageable input clutches and a plurality of meshing gear pairs downstream of the input clutches between the input clutches and the transmission output shaft. In most dual clutch arrangements, the gear section includes a central or main shaft aligned with the input shaft and output shaft and two countershafts disposed parallel with the input shaft. Meshing pairs of gears are mounted on the center shaft and on each of the countershafts. The gear pairs are interconnected between the shafts by synchronizers or a mechanical clutch mechanism. The dual input clutch arrangement permits the on-coming speed ratio to be synchronized prior to the power path being moved from one head gearset to another by way of the selectively engageable input clutches. This permits ratio interchanging without torque interruption, which is normally found in single clutch type transmissions.
In a dual clutch transmission which will produce six forward speeds and one reverse speed, the system requires two selectively engageable input clutches, seven and one-half pairs of external gears, one single synchronizer, and three two-way synchronizers. The seven and one-half pairs of gears consists of two head gear set pairs and one pair for each forward ratio, other than direct, and one and a half pair for reverse. In other words, an idler gear must be installed somewhere within the reverse gear train.